Generally, at least one printed circuit board (PCB) is employed in an electronic device, and various shaped elements are mounted on the PCB. In order to inspect defects of these elements, a three-dimensional shape measurement apparatus is typically used.
A conventional three-dimensional shape measurement apparatus illuminates light to a measurement target such as a PCB by using an imaging optical system, and image-captures a reflection image thereof using a camera. Then, a three-dimensional shape based on the height of the measurement target is measured using the captured reflection image.
Conventional imaging optical systems may be configured in various configurations. An optical triangulation method, a stereo method, etc. among the various configurations may be employed in the imaging optical system.
The optical triangulation method is a method using such as a bucket algorithm after acquiring a grating pattern, and widely used at present. However, this method has a problem that the height that is measurable is restricted by a pitch of a grating generating the pattern image.
The stereo method uses a stereo camera. Just as a person's perspective to an object can be perceived by synthesizing information input through two eyes into distance information, a stereo camera may also calculate three-dimensional distance information by capturing images from two cameras.
That is, a three-dimensional shape may be measured by using two or more images obtained by photographing at different positions. Particularly, in the two images including texture of a measurement target on a real space, position information of the measurement target in the real space of the measurement target is obtained by using a geometric structure based on the texture, to thereby measure the three-dimensional shape of the measurement target.
Thus, in case that the measurement target has texture, the three-dimensional shape of the measurement target may be measured based on the texture, but in case that the surface of the measurement target is smooth, since it is impossible to use a geometric structure based on the texture of the measurement target, the stereo method may be unavailable.